This invention relates generally to pulleys or sheaves which are lagged, that is, provided with special wear-resistant or friction surfaces, and more particularly to multi-part sheaves of the type having facings in their grooves, adapted for engagement by the strand material which is being handled.
In the past there have been many proposals and constructions for minimizing the friction and wear on pulleys and sheaves, as by providing metal or rubber, or rubber-like facings which are adapted for enagement with the belt or strand material passing over the pulley or sheave.
In the case of pulleys or rollers where the wear-resistant or other facings comprised metal overlays, or plates or lag strips which were attached to the pulley surfaces by suitable fastenings, when the wear strips or facings become worn or no longer useful, they were merely replaced by new strips or facings, thus saving the cost of discarding the entire pulley or sheave, as well as the expense represented by down time, labor, etc.
It has been common practice, in the handling of strand material which could cause excessive wear, to employ hardened facings, platings or inlays of wear-resilient metal, as for example chromium, carbide, etc. Surprisingly, these hardened facings would also ultimately show appreciable wear even with soft strand material, for the reason that the strand material was always presenting a new surface, and the amount of wear on any given section of the strand was infinitesimal. Moreover, the presence of dirt, grit and the like on the strands acted as an abrasive that was quite effective against hard metals.
Additionally, the use of particualarly hard metal inserts always represented an appreciable cost, since the special alloys, sintering and other processes etc. were not especially economical.
Often the replacement of wear-resistant surfaces of metal and the like on a pulley or sheave required the services of a skilled mechanic, and even though special provision was made for quick removal there was still involved a certain amount of down time of the equipment.
Where the pulleys or sheaves were disposed in somewhat inaccessible locations, the dismantling of portions of the equipment was sometimes necessary in order to reach the worn component and effect the replacement. Moreover, in the case where the worn component was in a cramped space, the replacement did not always proceed as quickly as could be desired.